If you are talking about gambling then it can be any site because its only about like and not because of any particular site.And if its about investment in gambling site then thats a really good return.Here are some sites like crypto-games.net,fortunejack or moneypot,have you invested in one of these.
maybe he means investing in gambling site, because he says that he "invested" 1mbtc and a profit of up to 8mbtc, if you forget which website you use to invested. you can see the list of gambling sites that accept investment facility in gambling section, you might find the site again, and tell me what it gambling site, and we can give it a try